A method for bonding an electrode of an electronic component, such as a semiconductor die, and an electrode in a circuit pattern on a circuit board is described in Japanese Patent Application Publication No. H09-326416, through the formation of a solder bump on an electrode pad of the electronic component, positioning the electronic component such that the formed solder bump faces down toward the electrode on the circuit board, and heating the solder bump, thereby bonding the electrodes. A method for bonding an electrode of an electronic component is also described in Japanese Patent Application Publication No. H10-150075. This publication describes a flip-chip bonding method of applying an electrically conductive bonding agent over a surface of a gold bump formed on an electrode surface of an electronic component such as a semiconductor die, flipping the semiconductor die to press the gold bump against an electrode of a circuit board, and then heating the bonding portion to bond the electrode of the semiconductor die to the electrode of a circuit pattern of the circuit board.
However, when attempting to bond electronic components in a three-dimensional stacking manner using soldering as with the conventional technique described in Japanese Patent Application Publication No. H09-326416, a previously bonded portion can often be fused due to heat applied when bonding, reducing reliability in bonding. Thus, various methods using a metal paste including ultrafine metallic particles have been proposed as a method of bonding electrodes without using solder bumps.
Japanese Patent Application Publication No. H09-326416 proposes a method of electrically bonding a semiconductor element and a circuit board, by forming a ball of a silver fine particle paste prepared by dispersing ultrafine silver powder in a solvent on a terminal electrode of a circuit board, bonding an electrode of a semiconductor element onto the ball formed on the terminal electrode of the circuit board in a face down method, and then sintering at a temperature of 100 to 250 degrees Celsius after a solvent such as toluene in the silver fine particle paste is evaporated. It is described that, according to this method, when the sintering temperature is from 200 to 250 degrees Celsius, the electrical bonding can be realized by sintering for 30 minutes in a hot-blast stove.
Japanese Patent Application Publication No. 2006-54212 describes a method of metal bonding, by printing a metal nanoparticle paste including metal nanoparticles having an average particle diameter of 30 nm or smaller and a dispersant over a surface of an electrode of a substrate, then heat curing the metal nano paste to form a metal nanoparticle film of the sintered metal nanoparticles over the surface of the electrode of the substrate, and carrying out ultrasonic bonding of a bump formed on an electrode of a semiconductor die to the metal nanoparticle film. It is described that, according to this method, the metal nanoparticles are fusion bonded to each other by the heat curing where the metal nanoparticle paste applied to the electrode on the substrate is heated up to and retained at 250 degrees Celsius using a heating device for 30 minutes, thereby forming the metal nanoparticle film over the electrode.
Japanese Patent Application Publication No. 2006-202938 discloses a method of bonding a metal layer of a semiconductor element and a metal substrate using a metal nano paste made of ultrafine particles of metal having an average diameter of 100 nm or smaller dispersed in an organic solvent. According to this bonding method, the metal included in the metal layer of the semiconductor element, the metal substrate, and the metal nano paste is one of metals including gold, silver, platinum, copper, nickel, chromium, iron, lead, and cobalt, an alloy including at least one of the metals, or a mixture of the metals or the alloy, and the metal layer of the semiconductor element and the metal substrate are bonded with a bonding layer interposed therebetween, which is formed by volatilizing the solvent to agglutinate the ultrafine particles by applying heat, pressure, or a combination thereof. Japanese Patent Application Publication No. 2006-202938 describes that, when a silver metal layer of the semiconductor element is bonded onto a copper metal substrate using a silver nano paste as the metal nano paste, the silver metal layer of the semiconductor element and the copper metal substrate can be bonded by applying a pressure such that a plane pressure between the semiconductor element and the metal substrate is on the order of several hundreds kPa to several MPa, and heating up to about 300 degrees Celsius.
Moreover, Japanese Patent Application Publication No. H10-150075 describes a flip-chip bonding method using an electrically conductive bonding agent, leveling gold bumps formed on an electrode of a semiconductor die to a height within a range of variations of 5 μm, and by correctly controlling a distance to an electrically conductive bonding agent. When the semiconductor die is flipped, an adequate amount of the electrically conductive bonding agent can be transferred to a tip end of a gold bump, and thus it is possible to prevent defects such as a bridge and a bonding defect.
According to the conventional techniques described in Japanese Patent Application Publication No. H09-326416 and Japanese Patent Application Publication No. 2006-202938, when bonding electronic components such as electrodes of semiconductor elements using a metal nano paste, it is necessary to apply a pressure to a bonding surface and maintain a temperature of about 200 to 300 degrees Celsius for 30 to 60 minutes. However, when bonding a circuit board of a semiconductor die, the bonding of a large number of semiconductor dies is required to be carried out in a short period of time. Therefore, maintaining such conditions for such a long period of time in the middle of a bonding step significantly reduces production efficiency.
According to a method described in Japanese Patent Application Publication No. 2006-54212 for forming a metal nanoparticle film over a substrate electrode and metal bonding a bump formed on the electrode of the semiconductor die to the film by ultrasonic bonding, a force exerted on the semiconductor die or the circuit board when bonding increases as the metals are bonded by ultrasonic bonding. However, with the recent demand for thinned semiconductor devices, semiconductor dies and circuit boards have become extremely thin and may be damaged by such a load when bonding. Therefore reduction of the bonding load is desirable.
According to the conventional technique described in Japanese Patent Application Publication No. H10-150075, an apparatus and a step of applying electrically conductive bonding agent for bonding between an electrode of a semiconductor die and an electrode of circuit board. As described, in order to bond the electrodes well, a variation in height of gold bumps formed on the electrode of the semiconductor die must be suppressed, and an adequate amount of electrically conductive bonding agent must be transferred to a tip end of a minute gold bump. This makes the apparatus complicated for controlling a position of a gold bump when forming the gold bump and transferring the electrically conductive bonding agent.
An object of the present invention is to provide an apparatus and a method, whereby the bonding load between an electrode of a semiconductor die and an electrode of a substrate can be reduced, and bonding between the electrodes can effectively be carried out in a simple and easy way.